1. Field of the Invention
An encoder for encoding light moving in the visible or infrared spectrums. In accordance with the present invention, the amount of light transmitted through a grating which has alternating opaque and translucent or transparent divisions thereon can be discerned. Depending on the particular embodiment selected, the present encoder can detect both motion and direction, as well as render a reference. The present invention is easily adapted for use with linear, arced, or any other type of grating. Tedious manual alignment of the grating with respect to other elements of the encoder can be eliminated. Within the scope of the present unity of invention, inclusion of the gradient index lens reflector eliminates the physical mask required which has previously been mandated for precision sensing of light transmitted through gratings. Further, the present encoder has been found to eliminate or minimize spherical aberration commonplace in the prior art.
2. Description of the Previous Art
a) U.S. Pat. No. 3,524,067-West discloses a compact line grating position sensing device. In a first embodiment, West requires at least one traditional plano-convex lens while in another and more preferred embodiment, a pair of conventional planar convex lens must be utilized to focus the light passing through the grating. West teaches that traditional glass lens having curved faces are required to focus light, before his invention can be practiced. Moreover, U.S. Pat. No. 3,534,067 is limited to position sensing.
b) U.S. Pat. No. 3,496,364-Foskett discloses a linear encoder having a fringe pattern produced by optical imaging. In accordance with Foskett, the combination of a traditional convex lens, a right angle prism and a pentaprism is required to bend the beam of light to the required parameters, before the invention can be practiced. Due to the design of U.S. Pat. No. 3,496,364, not only is it cumbersome to practice, but it is virtually impossible to keep its components in proper working alignment in an industrial setting. Thus, it appears any attempt to provide perpetual detection of any precisely and minutely refined motion or direction, if possible at all, is at best short-lived.
c) U.S. Pat. No. 4,180,703-Cialone, et. al., discloses a bi-directional, self-imaging grating detection apparatus which is especially useful for ink jet printers. Cialone's grating mandates two sets of opaque lines thereon, with one set being laterally offset from the other, and preferably, at an angle of 45 degrees relative to the other set. Importantly, U.S. Pat. No. 4,180,703 directs its source-detectors be aligned specifically with each separate set of opaque lines, on the grating, as well as its preferably concave reflective surface, for both motion and direction to be detected. Additionally, Cialone also requires the distance form its reflective spherical segment surface to the grating be equal to the radius of curvature of the spherical segment surface.
d) Based upon the information available to applicant, the current state-of-the-art technology for incremental encoders typically utilizes various combinations of housing assemblies, light sources, code disks, physical masks, photodetector assemblies and electronics boards. Please see, BEI Motions Systems Company's "Optical Design Guide" (copy to be included with applicant's 37 C.F.R. Section 1.56 Disclosure Statement). Although identical scientific precepts are applied to the functionality of either rotary or linear encoders, it appears rotary encoders dominate current usage. Examples of industries presently employing such encoders include machine control, process control, robotics, food processing and laboratory instrumentation, to name a few.